1. Field of the Invention
The present invention generally relates to printers, and more particularly, to a printer with an improved power-failure restart function.
2. Description of the Background Art
A cash register is provided with a printing mechanism for printing a name, department, price and the like of a sold commodity on a receipt sheet. Furthermore, the case that power is disconnected, for example, due to a power failure, the cash register has been adapted to automatically continue the operation which has been once interrupted by the failure, once power is restored. This occurs because the operation state of the cash register has been stored with various flags in a backed-up memory. Upon resumption of power, the cash register is returned to the operation state it was in when the failure occurred by returning such flags to resume the interrupted operation.
Assuming that there is to be provided a printing mechanism capable of subsequently printing characters such as letters or symbols which were being printed when power was disconnected, it is necessary to control a printing head and the like, with high precision so as to precisely replace the printing head to the position it was in when the power failed. Insufficient control precision for the printing head or the like may result in a shear in printing and prevent printing of a regular character. Such high precision control entails, however, not only increased cost but a larger, more complicated apparatus for the cash register.
In the above described cash register, therefore, the processing operation of the printing mechanism is controlled as follows, when the power failure is restored. FIG. 12A is a plan view showing a printed receipt sheet 1. Assuming that the power supply is disconnected due to a power failure when a character 3 is being printed on line 2, then, a flag representing that the mechanism is in process of printing has been raised in the cash register. Thereafter, when the failure is restored with resumption of power, in accordance with the flag, a cross-out printing is performed on the line 2, or horizontal lines "-" are superposed over the entire line 2 as shown in FIG. 12B. Then, the contents of the interrupted line are printed on line 4, which should have been printed on line 2. Subsequently, further operation, including printing on the following lines will be continued.
When the above described cash register is disconnected from the power supply due to a power failure, for example, in printing a blank 6 so as to subsequently print Y1,000 dep. (dep. is abbreviation for deposit) on line 5 close to the right side of a receipt sheet 1 as shown in FIG. 13A, the printing operation will be controlled as follows. That is, on line 5, the contents having been printed before the blank 6 are all blanks so that the printing operation has been interrupted without printing anything on the line 5. However, the resumption of power causes unnecessary cross-out printing to be made on line 5 and in turn the contents which should have been printed on the line 5 are printed on line 7, as shown in FIG. 13B. Therefore, blank characters are unnecessarily crossed out which makes the printed contents less legible, as well as wastes the receipt sheet 1 since blank space has been unnecessarily crossed out by printing on the line 5.